1. Field of the Invention
The present invention relates to a gimbaled compliant guide for tape drives. More particularly, the invention is a compliant guide which is pivotably mounted to accommodate variance in the path of a moving tape.
2. Discussion of the Related Art
Web and tape guiding apparatus are well known. Perhaps the most common use of such an apparatus is for guiding tapes in magnetic tape drives over a magnetic read/write head. Guiding of the tape over the head is critical to the writing of data to and the reading of data from the magnetic tape. A typical magnetic tape drive includes several elements in the tape path to ensure proper alignment and operation of the tape and head. For example, the tape path of the IBM 3480/3490 tape drives includes a supply reel inside a tape cartridge, a vibration decoupler, a cleaner blade, an arcuate supply side air bearing surface, a magnetic read/write head, an arcuate storage side air bearing surface, a tension transducer, a storage reel, and tape edge guides along the sides of the bearing surfaces. The tape guides physically align the lateral position (i.e. in the direction of the tape width) and slope (i.e. the change in height of the tape over the bearing surface) of the tape relative to the read/write head. Lateral positioning maintains proper alignment between the read/write elements of the head and the data tracks on the magnetic tape. Slope control minimizes the skew between bits written on the tape and the recording elements of the read/write head. The tape guides are located along the arcuate bearing surfaces because the tape in such proximity can support a larger guiding force without collapsing than can a freely suspended tape.
Different types of edge guides are known. One known type of edge guide is a fixed open channel guide, in which rigid flanges are attached to the tape bearing surfaces. The flanges are fixed in position and physically contact the edge of the tape to align the tape relative to the read/write head. Because the flanges are fixed, the distance between them must be large enough to accommodate the width of the tape, which varies as a result of manufacturing tolerances. To accommodate the maximum width of the tape there must be considerable lateral "play" of the tape between the flanges, resulting in sloppy positioning of the tape and thereby burdening the head servo also maintaining proper alignment between the read/write elements of the head and the data tracks on the magnetic tape.
One type of open channel guide includes a roller with parallel edge guiding flanges. The roller can pivot axially to change the direction of tape movement. The flanges are fixed to the roller, resulting in the aforementioned problems. Examples of pivoting rollers are disclosed in U.S. Pat. Nos. 4,770,550; 4,51S,134; 4,403,720; 4,122,985; 3,949,919; and 3,608,796.
An alternative to fixed guides which eliminates the lateral play between the tape and the head is referred to as a "compliant" edge guide. Such a guide uses a leaf spring or other laterally compliant mechanism to maintain the tape in contact with an opposing, fixed edge guide. The compliance of the guide accommodates variations in tape width, as well as variations in tape slope due to imperfect or changing tape path alignment. Examples of compliant guides are disclosed in U.S. Pat. No. 3,317,104, and in the following articles published in the IBM Technical Disclosure Bulletin: Johnson, "Compliant Tape Guide", Vol. 14, No. 2, July 1971, p. 399; Griffiths, "Continuous Compliant Tape Guide", Vol. 15, No. 8, January 1973, p. 2502; Bradley et al., "Web Slitting Device", Vol. 17, No. 7, December 1974, pp. 1860-61; Winarski, "Tape Guiding Analysis", Vol. 24, No. 11b, April 1982, pp. 5776-77; Andresen et al., "Tape Guide Design", Vol 27, No. 7B, December 1984, pp. 4360-61; Johnson et al., "Antimodal Compliant Tape Guide", Vol. 26, No. 7A, December 1983, p. 3398; Corradini et al., "Tape Guide Assemblies with Weighted Buttons", Vol. 31, No. 3, August 1988, pp. 232-233; Winarski, "Web-Guiding Stress Functions", Vol. 25, No. 4, September 1982, p. 2069; Clegg et al., "Compliant Tape Guide", Vol. 25, July 1982, pp. 809-810; Clegg et al., "Air Bearing Tape Guide", Vol. 25, No. 1, June 1982, pp. 447-48; Andresen et al., "Tape Tension Control", Vol. 25, No. 1, June 1982, pp. 444-46.
Perhaps the most well known of the compliant tape guides is shown in Garcia et al., "Compliant Guide Assembly with High Wear Resistance Contact Pads", Vol. 25, No. 5, October 1986, pp. 2126-27, which discloses the laterally compliant tape guides used in the IBM 3480/3490 tape drives. These compliant guides include wear resistant contact pads made from a material such as ferrite or alumina to prevent them from abrading and thereby contaminating the tape drive. The pads are mounted at the ends of stainless steel leaf springs such that the pads are adjacent the arcuate bearing surfaces to engage the edge of the tape as it passes thereover, and to gently urge the tape into proper lateral position.
A heretofore unrecognized problem with both fixed and compliant edge guides is their inability to comply with changes in the slope of the tape caused by alterations in the tape path, such as a wobbling tape reel. More specifically, if the guiding flange or contact pad does not lie in the plane formed by the arc of the tape edge over the bearing surface, contact between the tape edge and the flange may occur at a single point rather than along the entire span of the guide. Single point contact concentrates the stress on the tape and may result in tape wear and the generation of particulate matter. Such particulate matter in the tape path abrades the magnetic head, resulting in a loss of signal amplitude and separation of the head and tape (referred to as "dropout").